Inspection apparatus and inspection method

ABSTRACT

A defect inspection apparatus emits light to a test object, detects reflected of scattered light from the test object and detects a defect in the test object The apparatus comprises a temperature-controlled part accommodating section that accommodates parts having a need for controlling a temperature, which is out of a plurality of parts in the defect inspection apparatus. A first temperature measuring instrument measures a temperature in the temperature-controlled part accommodating section; and a temperature control unit controls a temperature of the interior of the temperature-controlled part accommodating section at a prescribed temperature according to the temperature measured by the first temperature measuring instrument. Accordingly, a defect inspection apparatus can efficiently perform temperature control without involving an enlarged size can be achieved.

This application is a Continuation of U.S. application Ser. No.11/989,018, filed on Jan. 18, 2008, now U.S. Pat. No. 8,102,522, whichis the U.S. National Phase under 35 U.S.C. §371 of InternationalApplication No. PCT/JP2007/063126, filed on Jun. 29, 2007, claimingpriority of Japanese Patent Application Nos. 2006-180638, filed on Jun.30, 2006 and 2007-092779, filed on Mar. 30, 2007, the entire contents ofeach of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an inspection apparatus and aninspection method. The present invention is suitable, for example, to adefect inspecting apparatus for checking for the presence of minuteforeign matter and other types of defects by using an optical system,such as a semiconductor inspecting apparatus, as well as a defectinspection method.

BACKGROUND ART

As semiconductor circuits are becoming increasingly fine, minute foreignmatter on semiconductor substrates becomes to affect the quality ofsemiconductor products.

As a technology for detecting this type of foreign matter on thesemiconductor substrates, Patent Document 1 discloses an inspectionapparatus and inspection method that improve detection sensitivity and athroughput by achieving high-efficiency linear illumination from adirection in which diffracted light is not delivered so as to reducelight diffracted from a pattern and by enabling thresholds to be setaccording to pattern-depending signal variations.

Patent Document 2 discloses an inspection apparatus that comprises aunit for storing the relation between temperatures measured in advanceor calculated through simulation and focused point offsets, a unit forpredicting a focused point offset from this relation betweentemperatures and focused point offsets according to a temperaturedetection result obtained by a temperature detecting unit, and a unitfor correcting a focused point offset according to the predictionprovided by that unit.

-   Patent Document 1: Japanese Patent Application Laid-open Publication    No. 2000-105203-   Patent Document 2: Japanese Patent Application Laid-open Publication    No. 2002-090311

DISCLOSURE OF THE INVENTION

In the prior art, however, there is no consideration for a case in whichthe relation between actual variations due to temperatures and focusedpoint offsets is not constant.

For example, it is apparent that different members used in a defectinspection apparatus respond to a change in temperature at differentspeeds and causes different amounts of variations. Accordingly, theamount of variations, that are its comprehensive result, varies as thetemperature changes with time.

The time elapsed after the temperature changes may be minute orsufficient, however, the difference between the amount of variations,which are a comprehensive result, and an amount of prediction is withinthe depth of focus of an optical inspection system, the sensitivity ofthe inspection apparatus drops only a little.

If the amount of variations, which are a comprehensive result, isgreater than the depth of focus of the inspection optical system withthe amount of prediction considered or if the amount of variations issmall at present but the depth of focus, which is given by “z=±λ/2NA²”may become small due to technological innovation in the future, the dropof the inspection sensitivity of the apparatus for temperature changescan be no longer neglected.

To prevent this drop of the inspection sensitivity, it is necessary tosuppress the amount of variations, which is a comprehensive result.

The use of a low thermal expansion material can be considered as a unitfor suppressing the amount of variations caused by temperature changes,and temperature control can be considered as a unit for suppressingtemperature changes.

However, the former unit is problematic in that the weight of theinspection apparatus is significantly increased, increasing burdens onthe apparatus manufacturing line and a semiconductor line.

As an example of the latter unit, temperature control technology hasbeen developed to maintain high precision in wafer overlayingpositioning and the ease of imaging.

Specifically, an entire exposing apparatus is covered with a temperaturecontrol chamber, and temperatures of a measuring optical path space, astage, structural supporting bodies, a lens, and a structural supportingbody of the lens are controlled by individual chambers.

However, differences in positional precision demanded for targets,differences in optical structures, and different thermal sources make itdifficult to apply the above temperature control technology to a defectinspection apparatus without alternation.

For example, the use of a temperature control chamber that covers anentire inspection apparatus enlarges the apparatus, resulting in largefootprints. Therefore, burdens on the apparatus manufacturing line andsemiconductor line are increased.

Technology that can efficiently control temperature while preventing theinspection apparatus from being enlarged is necessary.

An object of the present invention is to provide a defect inspectionapparatus and a defect inspection method that can efficiently controltemperature without involving an enlarged size.

In a defect inspection apparatus and a defect inspection methodaccording to the present invention that emit light to a test object anddetect reflected or scattered light to check for a defect in the testobject, a plurality of parts that need temperature control are selectedfrom a plurality of parts in the defect inspection apparatus and placedin a temperature-controlled part accommodating section, the temperaturein the temperature-controlled part accommodating section is measured,and a temperature control unit performs temperature control so that theinterior of the temperature-controlled part accommodating section iskept at a prescribed temperature.

According to the present invention, a defect inspection apparatus and adefect inspection method that can efficiently perform temperaturecontrol without involving an enlarged size can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing to show an entire structure of the defect inspectionapparatus of the first embodiment in the present invention.

FIG. 2 is a drawing to illustrate the principle of the first embodimentof the present invention.

FIG. 3 is an operation flowchart for temperature control in the firstembodiment of the present invention.

FIG. 4 is a drawing to illustrate an illumination to a sensor projectingsurface on a substrate under inspection from three directions.

FIG. 5 is a top view of an illumination optical system.

FIG. 6 is a structural drawing of a temperature control system in thefirst embodiment.

FIG. 7 is a graph to illustrate the inspection sensitivity stabilityachieved by temperature control according to the present invention.

FIG. 8 is a drawing to show a schematic structure of the temperaturecontrol system in a second embodiment of the present invention.

FIG. 9 is a drawing to show a schematic structure of the temperaturecontrol system in a third embodiment of the present invention.

FIG. 10 is a drawing to show the schematic structures of the foreignmatter detection optical system and focus detection optical system ofthe foreign matter inspection apparatus.

FIG. 11 is a block diagram of an embodiment for compensating for anatmospheric pressure and temperature.

FIG. 12 is a graph to indicate temperature variations and changes in thefocus Z coordinate under the condition where temperature is notcompensated.

FIG. 13 is a graph to indicate the relation between the temperature andthe focus coordinate is linear.

FIG. 14 is a graph to indicate temperature variations and Z compensatedvalues for temperatures.

FIG. 15 is a graph obtained by subtracting the characteristics in FIG.12 from the characteristics in FIG. 14. That is, FIG. 15 is a graph toindicate a focus error in compensation for temperatures.

FIG. 16 is a graph to indicate atmospheric pressure variations andchanges in the focus Z coordinate under the condition where atmosphericpressure is not compensated.

FIG. 17 is a graph to indicate the relation between the atmosphericpressure and the focus coordinate is linear.

FIG. 18 is a graph to indicate atmospheric pressure variations and Zcompensated values.

FIG. 19 is a graph obtained by subtracting the characteristics in FIG.16 from the characteristics in FIG. 18. That is, FIG. 19 is a graph toindicate a focus error in compensation for atmospheric pressures.

LEGEND

-   -   1: substrate under inspection (wafer), 2: chip, 3: slit beam, 4:        area detected by an image sensor such as a TDI sensor, 100:        illumination optical system, 101: laser light source, 102:        concave lens, 103: convex lens, 104: optical filter group, 105:        mirror, 106: optical branching element (direction 11), 107:        illumination lens, 108: incident mirror, 109: angle-of-elevation        switching mirror, 110: direction-11 lighting fixture, 114:        optical branching element (direction 12), 115: optical branching        element (direction 12), 120: direction-12 lighting fixture, 130:        direction-13 lighting fixture, 200: inspection optical system,        201: objective lens, 202: Fourier transform face, 203: imaging        lens, 204: varifocal lens group, 205: detector, 206: sensor Z        driving mechanism, 207: spatial filter control unit, 208: lens        driving control unit, 209: detected field, 210: auto focus unit,        300: stage unit, 301: X stage, 302: Y stage, 303: Z stage, 304:        angle stage, 305: stage controller, 400: control system, 401:        driving processing system, 402: image processing system, 403:        display system, 404: input system, 500: base, 501: stone surface        plate, 502: optical surface plate, 503: second optical surface        plate, 600: temperature control system, 601: temperature control        unit, 602: control CPU in the temperature control unit, 603:        temperature measuring instrument, 604: temperature-controlled        part accommodating section, 605: heat radiating unit, 611:        outward pipe of the temperature control medium, 612: inward pipe        of the temperature control medium, 613: flow path in the main        body of the temperature control unit, 614: clean filter, 615:        fan filter unit (FFU), 616: airflow (of clean air), 617 a, 617        b: heat insulating valve, 1500: focus detection optical system,        1501: focus detection light source, 1502: focus detection        phototransmitting optical system, 503: photoreceving optical        system, 1504: focus detection sensor, 1505: focus signal        processing unit, 1600: atmospheric pressure and temperature        sensor system, 1601: atmospheric pressure sensor, 1602:        atmospheric pressure data logger, 1603: temperature sensor,        1604: temperature data logger

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

First Embodiment

A defect inspection apparatus in a first embodiment of the presentinvention will be described with reference to FIGS. 1 to 7.

In the embodiment described below, a surface foreign matter inspectionapparatus will be used as an example of the defect inspection apparatus.

The first embodiment of the present invention suppresses variations infocused positions through temperature control to ensure stableinspection sensitivity, reduces the number of times an apparatus hasneeded to stop on an apparatus manufacturing line or semiconductor lineto calibrate inspection sensitivity due to variations in focusedpositions, achieves efficient heat exchange while reducing the price ofthe apparatus and footprints by devising an arrangement of theapparatus, and eliminates the use of a fan filter unit (FFU) by usingtemperature-controlled air as clean air.

FIG. 1 shows the entire structure of a defect inspection apparatus towhich the present invention is applied. The defect inspection apparatusin the first embodiment, shown in FIG. 1, comprises a stage unit 300, anillumination optical system 100, at least one inspection optical system200, a control system 400, and a temperature control system 600 (shownin FIG. 2).

The stage unit 300 has an X stage 301, a Y stage 302, a Z stage 303, anangle stage 304, and a stage controller 305. When a wafer 1 is placed onthe stage unit 300, the angle stage 304 performs alignment in an angulardirection and the Z stage 303 performs alignment in the Z direction.

When the wafer 1 is scanned, the X stage 301 performs scanning in the Xdirection, the Y stage 302 feeds the wafer 1 in the Y direction, andthen the X stage 301 performs scanning in the reverse direction. Thiscycle is repeated.

The illumination optical system 100 has a common optical path and aplurality of illuminating unit, which are a lighting fixture 110 (firstilluminating unit) in a direction 11 (shown in FIG. 5), a lightingfixture 120 (second illuminating unit) in a direction 12 (shown in FIG.5), a lighting fixture 130 (third illuminating unit) in a direction 13(shown in FIG. 5).

Parts in the common optical path include a laser light source 101, aconcave lens 102 and convex lens 103 that fulfill the role of a beamexpander, an optical filter group 104 including an ND filter and awavelength plate, and a mirror 105 for routing an optical path.

The illumination optical system 100 has an optical branching element (ormirror) 106 that can be switched to a transparent glass plate as a partof a lighting fixture in each direction, an illumination lens 107, anincident mirror 108 for directing the optical path in the verticaldirection, and angle-of-elevation switching mirrors 109.

The beam that has passed through the illumination lens 107 is directedas slit beams 3 from three directions 11, 12, and 13 on the wafer 1 sothat its short-side direction matches the array direction of chips 2, asshown in FIG. 5.

To perform defect inspection at high speed, the slit beams 3 aredirected so that the scanning direction X on the X stage 301 matches theshort-side direction and the scanning direction Y on the Y stage 302matches the long-side direction.

That is, when the amount of feed in the Y direction is increased, thetotal amount of scanning on the stages can be reduced.

The illumination intensity (power) of a beam light flux emitted from thelaser light source 101 can be controlled by using the ND filter of theoptical filter group 104 or the like.

The inspection optical system 200 comprises an objective lens 201, aFourier transform face 202, which is controlled by a spatial filtercontrol unit 207, an imaging lens 203, a varifocal lens group 204, whichis controlled by a lens driving control unit 208, and a detector 205,such as a TDI sensor. The inspection optical system 200 first directsthe slit illumination 3 to the wafer 1 and gathers generated light andscattered light with the objective lens 201.

An interfered part of diffracted light, which appears on the Fouriertransform face 202 dominated by repeated patterns on the wafer 1, isthen shielded by a spatial filter (not shown).

Light that has transmitted through the spatial filter undergoesmagnification ratio adjustment by the varifocal lens group 204.

Finally, the imaging lens 203 forms an image on the detector 205. Anarea that concurrently satisfies a detected field 209 (shown in FIG. 4)on the wafer 1 and a detected area 4 (shown in FIG. 4) is focused on thesensor of the detector 205.

When the slit beams 3 are directed to the wafer 1 on which various formsof circuit patterns are formed, reflected and scattered lights areejected from the circuit patterns and defects such as foreign matter onthe wafer 1. Reflected and scattered lights generated from the circuitpatterns are shielded by the spatial filter. Lights that havetransmitted through the spatial filter are focused on the detector 205and undergo photoelectric conversion.

The control system 400 comprises a driving control system 401 forcontrolling a driving mechanism and the sensor, an image processingsystem 402, a display system 403, and an input system 404.

The image processing system 402 comprises an A/D converter for dataresulting from photoelectric conversion by the detector 205, a datamemory, a difference processing circuit for obtaining a difference insignals between chips 2, a memory for tentatively storing a differentialsignal between chips 2, a threshold calculating part for setting apattern threshold, a comparison circuit, and an inspection resultstoring system for storing and outputting defect detection results suchas for foreign matter.

Furthermore, as shown in FIG. 6, units in the first embodiment of thepresent invention include an auto focus system 210 having optical pathsprovided separately from the objective lens 201 and inspection opticalsystem 200, an optical surface plate 502 on which to mount theinspection optical system 200, auto focus system 210, and illuminationoptical system 100, and a stone surface plate 501 on which to mount theoptical surface plate 502 and stage unit 300, and a temperature controlsystem 600 (shown in FIG. 2).

FIG. 2 illustrates the principle of the first embodiment of the presentinvention. As shown in FIG. 2, the temperature control system 600comprises a temperature control unit 601, a temperature measuringinstrument 603 (first temperature measuring unit), an outward pipe 611and an inward pipe 612 for supplying temperature-controlled airflow tothe main body of the apparatus, and a temperature-controlled partaccommodating section 604.

The temperature-controlled part accommodating section 604 occupies spacebetween the lower end of the stone surface plate 501 and the lower endof a sensor Z driving mechanism 206; the inspection optical system 200and auto focus system 210 are accommodated in the space.

Out of a plurality of parts in the defect inspection apparatus, thetemperature-controlled part accommodating section 604 accommodates aplurality of parts that need temperature control. Parts that do not needtemperature control are accommodated in a heat radiating unit 605.

That is, the parts constituting the defect inspection apparatus areclassified into parts that need temperature control and parts that donot need temperature control; the parts that need temperature controlare kept at a fixed temperature in a collective manner.

The heat radiating unit 605 in FIG. 2 accommodates at least the detector205 and other parts that become heat sources, and may accommodate adriving part (not shown) of the stage unit 300, the laser light source101, and the control system 400 and other parts that become heatsources.

Causes why the imaging position is shifted due to temperature changesare a first focal length change caused by a change in index ofrefraction on an optical path, a second focal length change caused bydeformation of the cylinder of the objective lens 201, and a third focallength change caused by deformation of the optical surface plate 502 orstone surface plate 501 and a positional change of the auto focus unit210 or objective lens 201 mounted on the optical surface plate 502 andstone surface plate 501.

In particular, the third focal length change varies at a start point andend point of the temperature change and during the duration of thechange, because the causative parts comprise a plurality of membershaving different thermal time constants.

Accordingly, if the present invention is not applied, it is difficult topredict the amount of change and make compensation, so periodiccalibration is needed to avoid unstable inspection sensitivity and theapparatus is forced to stop on the apparatus manufacturing line orsemiconductor line each time calibration is performed.

In the first embodiment of the present invention, since the temperaturesof the parts related to imaging position displacement (objective lens201, auto focus unit 210, stone surface plate 501, and optical surfaceplate 502) are fixed, that is, these parts (objective lens 201, autofocus unit 210, stone surface plate 501, and optical surface plate 502)are accommodated in the temperature-controlled part accommodatingsection 604 and controlled so that their temperatures are fixed, focallength changes (imaging position displacement) that are difficult topredict can be eliminated and thereby inspection sensitivity can be mademore stable.

If the apparatus temperature is controlled in the range around 23° C.,for example, as shown in FIG. 7, the inspection sensitivity isstabilized, so the number of times the apparatus has to stop on theapparatus manufacturing line or semiconductor line due to inspectionsensitivity calibration can be reduced.

In the first embodiment of the present invention, temperature-controlledclean air is supplied into the temperature-controlled part accommodatingsection 604 (in which a heat insulating material is used to prevent heatinflow from and heat outflow to the ambient space), as shown in FIGS. 2and 6, so the interior of the defect inspection apparatus can be keptclean without a fan filter unit (FFU) being installed.

Dust generated in the apparatus flows along an airflow 613 of the cleanair and is efficiently removed by a clean filter 614 (shown in FIG. 6).

To keep the interior of the defect inspection apparatus clean, the cleanair preferably circulates in the temperature-controlled partaccommodating section 604 and temperature control unit 601 in such a waythat the clean air is supplied downwardly.

The clean filter 614 is preferably disposed at an intermediate point inthe outward pipe 611 and immediately before the temperature-controlledpart accommodating section 604.

This is because the degree of cleanness can be made highest as comparedwhen the clean filter 614 is disposed in other places.

Incidentally, the clean air must flow in one direction, so the airflowcannot be circulated within the temperature-controlled partaccommodating section 604.

A slight temperature gradient is generated along the airflow 613 in thetemperature-controlled part accommodating section 604.

Here, a key point is that stable temperature around each target thatneeds temperature control rather than a uniform temperature distributionin the temperature-controlled part accommodating section 604.

When the temperature state including the temperature gradient in eachtarget that needs temperature control is stabilized, the stability ofthe inspection sensitivity can be improved.

FIG. 3 is an operation flowchart for temperature control in the firstembodiment of the present invention.

When power is turned on in step 1000 in FIG. 3, the temperature controlsystem 600 sets a temperature control medium to initial temperature t₀in step 1001 and flows the temperature control medium into thetemperature-controlled part accommodating section 604.

In step 1002, temperature t in the temperature-controlled partaccommodating section 604 is always monitored by the temperaturemeasuring instruments 603, and obtained temperature data is loaded intoa control CPU 602 in the temperature control unit through acommunication cable.

To keep the temperature in the temperature-controlled part accommodatingsection 604 at a fixed level, the control CPU 602 in the temperaturecontrol unit 601 controls the temperature of the air so that a deviationfrom a temperature range, which is set in advance by detectingtemperature changes, is eliminated.

Upon the startup of the temperature control unit 601, the control CPU inthe temperature control unit begins to flow air at the initialtemperature that is set in advance, and adjusts the temperature of theair while checking feedback from the temperature measuring instruments603.

That is, in step 1003, the control CPU 602 determines whether themeasured temperature t is within a prescribed temperature range (morethan t₀−Δt₀ but less than t₀+Δt₀). If the temperature t falls within theprescribed temperature, the sequence proceeds to step 1004, in which thetemperature of the temperature control medium is set to t₀+Δt₁ and thesequence returns to step 1002.

If the measured temperature t is not within the prescribed range in step1003, the sequence proceeds to step 1005, in which it is determinedwhether t₀+(t₀−t) is within the range of temperatures controllable bythe temperature control unit 601.

If t₀+(t₀−t) is within the range of temperatures controllable by thetemperature control unit 601, the sequence proceeds to step 1006, inwhich the temperature of the temperature control medium is set tot₀+(t₀−t) and the sequence returns to step 1002.

If t₀+(t₀−t) is not within the range of temperatures controllable by thetemperature control unit 601 in step 1005, the sequence proceeds to step1007, in which the temperature of the temperature control medium is setto a control temperature limit lower than t₀+(t₀−t) and the sequencereturns to step 1002.

Ideally, the temperature gradient is t₀+Δt₁ in the outward pipe 611, t₀in the temperature measuring instruments 603, and t₀+t₂ in the inwardpipe 612.

As described above, the air has a temperature gradient along the airflow613. Accordingly, the longer a physical distance from the temperaturemeasuring instruments 603 along the airflow 613 is, the lower thetemperature stability is.

The temperature measuring instruments 603 are thus preferably disposednear its target that needs temperature control; for example, it ispreferably grounded.

Furthermore, temperature characteristics, such as the amount of responsedisplacement and response speed, should be considered for temperaturevariations of each target that needs temperature control.

In the first embodiment, temperature variations of the stone surfaceplate 501 are largest, followed by the optical surface plate 502 andother parts (the auto focus unit 210 and objective lens 201) in thatorder, and the response speed is reduced in that order.

As the response speed is increased, more unstable temperatures arefollowed. As the response speed is decreased, a result of a moreaveraged unstable temperature appears as variations, so the effect issmall.

Accordingly, in the first embodiment, a position at which to dispose thetemperature measuring instruments 603 was set to a mountable position atwhich the sum of the distance from the objective lens 201 and thedistance from the auto focus unit 210 is minimized.

As described above, in the first embodiment of the present invention,the parts constituting the defect inspection apparatus are classifiedinto parts that need temperature control and parts that do not needtemperature control; all the parts that need temperature control areaccommodated together into the temperature-controlled part accommodatingsection 604 so that a fixed temperature is kept.

Therefore, it becomes easy to keep a fixed temperature, when comparedwith a case in which individual parts are temperature-controlledseparately by being heated or cooled, yielding an energy saving effect.

When compared with the case in which individual parts aretemperature-controlled separately by being heated or cooled, it sufficesto perform temperature control in a collective manner, reducing requiredtemperature detecting devices and simplifying temperature control.

In addition, there is no need to cover the entire defect inspectionapparatus, so it is not enlarged.

When the parts that need temperature control undergo temperature controlin a collective manner as in the first embodiment of the presentinvention, it become possible to reduce footprints by about 10% to 20%,when compared with a case in which the entire apparatus is covered witha temperature control chamber.

A heat insulating material may be used to thermally isolate all theparts together that need temperature control from the ambientenvironment.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIG. 8.

In the second embodiment of the present invention, a liquid is used asthe temperature control medium, the height of the apparatus is reducedso that the FFU can be mounted, and inspection sensitivity is improvedby eliminating optical path fluctuations by the use of airflows in theillumination optical system 100 and inspection optical system 200.

The basic structure is the same as in the first embodiment; that is, theparts constituting the defect inspection apparatus are classified intoparts that need temperature control and parts that do not needtemperature control, and the parts that need temperature control arekept at a fixed temperature in a collective manner.

Identical parts are therefore indicated by identical reference numerals,and only descriptions that differ between the first and secondembodiments will be given below.

On the optical surface plate 502 in FIG. 8, the illumination opticalsystem 100, at least one set of the inspection optical system 200, theauto focus unit 210, and a second optical surface plate 503 are mounted.

The stone surface plate 501 and the like are supported by bases 500. Tosimplify the drawing, columns for supporting the optical surface plate502 from the stone surface plate 501 are omitted.

The sensor Z driving mechanism 206 and detector 205 are mounted on thesecond optical surface plate 503.

The range accommodated by the temperature-controlled part accommodatingsection 604 is from the lower end of the optical surface plate 502 tothe upper end of the second optical surface plate 503.

In a broad sense, the stone surface plate 501 can also be included inthe temperature-controlled part accommodating section 604. Other membersare included in the heat radiating unit 605.

The interior of the temperature-controlled part accommodating section604 is monitored by the temperature measuring instruments 603. Obtainedtemperature data is loaded in a control CPU 602 in the temperaturecontrol unit 601 through a communication cable.

To keep the temperature in the apparatus at a fixed level, the controlCPU 602 in the temperature control unit 601 controls the temperature ofthe temperature control liquid so that a deviation from a temperaturerange, which is set in advance by detecting temperature changes, iseliminated.

This liquid circulates along the flow path 613; the liquid passesthrough the temperature control unit 601, outward pipe 611,temperature-controlled part accommodating section 604, and inward pipe612, and returns to the temperature control unit 601.

The liquid used for this temperature control is preferably, for example,pure water, fluorine-based inert liquid, hydro fluoro ether (HFE),ethylene glycol, or another substance that does not corrode the membersincluded along the flow path 613.

The temperature control liquid directly performs temperature control onthe stone surface plate 501, optical surface plate 502, and the secondoptical surface plate 503. The surface plates, the temperatures of whichare directly controlled, function as indirect temperature control unitsand control the temperature in the temperature-controlled partaccommodating section 604.

In the example shown in FIG. 8, a set of the temperature measuringinstrument 603 and temperature control unit 601 performs temperaturecontrol.

In this case, a device is preferably made for a place at which to mountthe temperature measuring instrument 603, as described later.

A plurality of sets of temperature control units 601, control CPUs 602in temperature control units, and temperature measuring instruments 603may be used to perform temperature control separately for the stonesurface plate 501, optical surface plate 502, and second optical surfaceplate 503.

In this case, the temperature measuring instruments 603 are preferablydisposed near the center of the flow path 613 of each surface plate.

The temperature control liquid in the second embodiment of the presentinvention lacks an air cleaning function as used in the firstembodiment.

Accordingly, the FFU 615 is preferably disposed in such a way that cleanair along an airflow 616 between the stone surface plate 501 and opticalsurface plate 502 blows dust near the surface of the wafer 1 off theapparatus.

If the clean air is directed in the direction of the airflow 616 (fromleft to right in FIG. 8), rather than downwardly, the FFU 615 may bedisposed next to the apparatus, enabling the height of the apparatus tobe reduced.

In the second embodiment of the present invention, it becomes easy tokeep a fixed temperature, when compared with a case in which individualparts are temperature-controlled separately by being heated or cooled,yielding an energy saving effect, as in the first embodiment.

In the second embodiment of the present invention, there is no airflowin the temperature-controlled part accommodating section 604, so opticalpath fluctuations in the illumination optical system 100 and inspectionoptical system 200 can be significantly reduced, improving thesensitivity stability.

A position at which to dispose the temperature measuring instruments 603in the second embodiment of the present invention is preferably set to aposition within the optical surface plate 502 at which the sum of thedistance from the objective lens 201 and the distance from the autofocus unit 210 is minimized.

This is because if the temperature measuring instruments 603 aredisposed at the same position as in the first embodiment, an ambienttemperature is measured.

In FIG. 8, part of the objective lens 201 and auto focus unit 210touches the airflow 616, but only their ends are brought into contactand most parts are temperature-controlled by internal thermalconduction.

In the second embodiment of the present invention, temperature isindirectly controlled, so the temperature controlled in thetemperature-controlled part accommodating section 604 is more stablethan in the first embodiment. However, the temperature in thetemperature-controlled part accommodating section 604 responds slowly totemperature control by the temperature control unit 601.

Consequently, variations in ambient temperature are highly likely toaffect the temperature-controlled part accommodating section 604 throughside walls.

For these reasons, a heat insulating material is preferably used for theside walls of the temperature-controlled part accommodating section 604.

The flow path 613 is preferably arranged near its upper surface of thesecond optical surface plate 503.

The reason for this arrangement is to prevent a temperature gradientfrom occurring in the second optical surface plate 503 due to the effectof the outside air and temperature variations of the detector 205.

For a similar reason, in the first optical surface plate 502, the flowpath 613 is disposed near its lower surface; in the stone surface plate501, the flow path 613 is disposed near its upper and lower surfaces asmuch as possible.

In this embodiment, each surface plate is holed so as to form theairflow. A temperature-controlled sheet may be attached to each surfaceplate instead of making holes so as to perform temperature control.

It is also possible to use both a holed surface plate and a surfaceplate to which a sheet is attached.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIG. 9.

In the third embodiment of the present invention, in addition to thetemperature control unit 601, heat sources in the apparatus are used fortemperature control, reducing burdens on the apparatus manufacturingline and semiconductor line caused by energy.

The basic structure is the same as in the first embodiment; that is, theparts constituting the defect inspection apparatus are classified intoparts that need temperature control and parts that do not needtemperature control, and the parts that need temperature control arekept at a fixed temperature in a collective manner.

Only descriptions that differ between the first and third embodimentswill be given below.

In FIG. 9, the temperature control unit 601 is connected to the heatradiating unit 605 (first heat radiating unit) via a pipe that isprovided with a heat insulating valve 617 a. The temperature controlunit 601 is also connected to an apparatus 618 (second heat radiatingunit) in the outside environment via another pipe that is provided witha heat insulating valve 617 b.

The temperature control unit 601 does not control the temperature of amedium by using only electric power; the control CPU 602 in thetemperature control unit 601 adjusts the heat insulating valves 617 aand 617 b and heat from the heat radiating unit 605 and apparatus in theoutside environment are used to control the temperature of the medium.

That is, a second temperature measuring unit measures the temperature ofthe heat radiating unit 605, and a third temperature measuring unitmeasures the temperature of the apparatus 618 in the outsideenvironment; when the temperature in the temperature-controlled partaccommodating section 604 controlled to be at a constant temperature,either the heat radiating unit 605 or the apparatus 618 in the outsideenvironment is determined to be suitable for heat exchange, and theoperation of opening and closing the insulating valves 617 a and 617 bis controlled so that the heat exchanging medium can be circulated.

This arrangement can not only reduce electric power consumed by thetemperature control unit 601 but also can reduce heat radiated from thetemperature control unit 601 and heat radiating unit 605, improving theenergy efficiency of the apparatus manufacturing line and semiconductorline.

In a variation of the third embodiment, a plurality of parts and regionsin the heat radiating unit 605 in the inspection apparatus areclassified into parts and regions with high generated heat temperaturesand parts and regions with low generated heat temperatures andaccommodated in a high-temperature part accommodating section and alow-temperature part accommodating section, each of which is equippedwith a temperature measuring unit and also provided with pipes andvalves to connect with the temperature control unit 601, and determineswhich section to be exchanged a heat according to the measuredtemperature.

In this arrangement, parts and regions that do not need temperaturecontrol can be used to fix the temperatures of parts that needtemperature control, enabling the temperatures to be controlled moreefficiently, that is, with less energy consumption.

In this variation, the apparatus 618 in the outside environment may beused for heat exchange, and an arrangement in which the apparatus 618 inthe outside environment is not used for heat exchange may be formed.

Although the above embodiments have been described by using a defectinspection apparatus that uses laser light to detect wafer defects, suchas foreign matter, dirt, cracks, crystal defects, COPs, and patterndefects, as an example, the present invention can be applied to not onlyapparatuses that use laser light to inspect foreign matter on the waferbut also defect inspection apparatuses that use other types of light.

Specifically, some optical systems use not only laser light but alsohalogen lamps, mercury vapor lamps, Xe lamps, etc., and other opticalsystems are electronic optical systems that use electronic beams. Thepresent invention can also be applied to defect inspection apparatusesusing these optical systems.

Test objects are applied not only to wafers used as semiconductorsubstrates but also to glass substrates used in flat panel displayunits, ALTIC substrates, sapphire substrates used in sensors and LEDs,disk substrates, etc.

The present invention can be applied to a wide range of inspectionapparatuses intended for surface inspection, mask inspection, bevelinspection, etc.

The temperature control according to the present invention can beperformed by using heating due to a heater as well as electronicrefrigeration and heating utilizing the Peltier effect or Seebeckeffect.

Fourth Embodiment

In this embodiment described below, the focus position changes accordingto, for example, the weather conditions including atmospheric pressureand temperature.

This embodiment relates to an inspection apparatus that checks forforeign matte, defects, and the like on a semiconductor wafer etc. in,for example, a semiconductor manufacturing process.

To increase a yield in a semiconductor manufacturing process byminimizing failures, it is usually important to detect foreign matterand defects on wafers in the process with high sensitivity, classifydetected results, determine causes, and take action accordingly.

An inspection apparatus (referred to below as the foreign matterinspection apparatus) is used to detect and classify these foreignmatters and defects. High sensitivity, high throughput, and highclassification performance are demanded for the foreign matterinspection apparatus.

The following documents relates to this type of foreign matterinspection apparatus.

-   Japanese Patent Application Laid-open Publication No. Sho 62    (1987)-89336-   Japanese Patent Application Laid-open Publication No. Hei 1    (1989)-117024-   Japanese Patent Application Laid-open Publication No. Hei 1    (1989)-250847-   Japanese Patent Application Laid-open Publication No. Hei 6    (1994)-258239-   Japanese Patent Application Laid-open Publication No. Hei 6    (1994)-324003-   Japanese Patent Application Laid-open Publication No. Hei 8    (1996)-210989-   Japanese Patent Application Laid-open Publication No. Hei 8    (1996)-271437-   Japanese Patent Application Laid-open Publication No. 2000-105203

The foreign matter inspection apparatuses disclosed in these documentsperform focus adjustment in order to obtain high sensitivity.

The focus position changes according to the weather conditions includingatmospheric pressure and temperature.

Specifically, changes in atmospheric pressure and temperature each causea change in air density, changing the index of refraction of air andthen changing the focus position.

Noting that changes in atmospheric pressure and temperature cause achange in focal position in an optical system, this embodiment wasdevised in the course of taking action against sensitivity variationsinvolved in the weather conditions.

As described above, an apparatus including an optical system usuallyneeds focus adjustment to obtain an optimum image.

With an exposing apparatus such as a stepper or scanner, the quality ofan image can be directly monitored through a through-the-lens (TTL);even if a focus change occurs in the exposure optical system due to anatmospheric pressure and temperature, the focus can be adjusted bymonitoring the image quality and thereby the focus changed by theatmospheric pressure and temperature can also be adjusted.

This arrangement is applied not only to an exposing apparatus but alsoto general apparatuses that can directly monitor image quality throughan optical system, such as for example a camera.

However, the foreign matter inspection apparatus cannot adjust the focusby a method in which image quality is directly monitored through amicroscopic optical system.

To solve this problem, a focus control optical system is provided inaddition to the microscopic optical system intended for foreign matterinspection.

To achieve focus adjustment by a detection optical system in the foreignmatter inspection apparatus, a Z coordinate at which signal intensity ismaximized, which is a performance index of the apparatus, is found bythe microscopic optical system in advance; a focus control opticalsystem then performs control so that the Z coordinate is maintained.

An operation for searching for the Z coordinate at which the signalintensity is maximized is a calibration operation rather than anoperation specific to the foreign matter inspection apparatus. Althoughit is necessary that the Z coordinate is frequently searched for so asto suppress the effect by focus variations to a minor level, thisoperation is complicated and drops the availability of the apparatus.

As described above, the focus adjustment in the foreign matterinspection apparatus involves problems described below.

A functional problem in the focus adjustment is that the optimum Zcoordinate at which the signal intensity is maximized varies withchanges in weather conditions including atmospheric pressure andtemperature, reducing the sensitivity.

A problem with a focus adjustment task is that the task is complicatedand takes much time (three to eight minutes).

To suppress the effect by focus variations to a minor level, the focusadjustment task needs to be performed frequently at time intervalsshorter than time intervals at which the atmospheric pressure andtemperature change.

According to measurements, the atmospheric pressure and temperature maychange at time intervals of about two hours. To avoid an effect by thischange, the focus adjustment operation must be performed about once perhour.

This embodiment addresses this problem with an object of alwaysmaintaining a maximum sensitivity and eliminating the focus adjustmenttask that would otherwise need to be performed to maintain highsensitivity.

Another object of this embodiment is to improve the availability of theapparatus by eliminating the focus adjustment task that would otherwisereduce the availability.

A first feature of this embodiment to achieve the above objects is thatattention has been focused on that a Z coordinate is changed by changesin atmospheric pressure and temperature, as described below.

First, according to the equation of state of a gas, “PV=nRT” holds.

(P=pressure [atm], V: volume (L), n: number of moles, R: gas constant(=0.082), T: absolute temperature [K])

Let n be w/M (w: mass, M: molecular weight) and V be w/d (d: density[g/L]), then the equation of state of a gas can be rewritten as“d=PM/TR” and further as “Δd=ΔPM/ΔTR”.

This unit that a change in air density is proportional to a change inatmospheric pressure and inversely proportional to a change intemperature.

According to the Gladstone-Dale equation, “N=1+d·r” then holds.

(N: index of refraction, d=density [g/L], r=Gladstone-Dale constant)

This unit that a change in air density is proportional to a change inindex of refraction in an optical system.

According to the Snell's law, a change in index of refraction finallybecomes a change in focal length (Z coordinate).

A second feature of this embodiment is that since an atmosphericpressure sensor and a temperature sensor are provided, a change in focusdue to a weather condition change can be comprehensively compensatedfor.

If, for example, only an atmospheric sensor or temperature sensor isused for compensation, it cannot be said that a change in focus due toweather condition changes is comprehensively compensated for.

However, it would be understood that, in an environment in which eitherthe atmospheric pressure or temperature is controlled, it suffices toprovide for compensation for a non-controlled parameter.

A third feature of this embodiment is that, in addition to stabilizing aZ coordinate by compensating for changes in atmospheric pressure andtemperature, the Z coordinate continue to be compensated so that themaximum sensitivity is always obtained.

The method for this is achieved by the following simple control. Anoptimum Z coordinate at which the signal intensity is maximized issearched for in advance, and the atmospheric pressure, temperature, andoptimum Z coordinate at that time (respectively referred to as thereference atmospheric pressure, reference temperature, and reference Zvalue) are used as three reference values; an atmospheric pressure andtemperature are measured at an arbitrary point of time at which todetect foreign matter; differences from the reference values are takenand converted to a Z coordinate, and the converted Z coordinate is addedto the reference Z value.

This embodiment is not limited to the foreign matter inspectionapparatus, but efficiently effected to maintain the maximum signalintensity without performing the complicated focus adjustment operationin comprehensive apparatuses in which a focus adjustment operationcannot be performed by a method of directly monitoring image quality anda microscopic optical system and a focus control optical system areprovided.

According to this embodiment described above, it suffices to search foran optimum Z coordinate once, after which the Z coordinate can becontrolled while variations in atmospheric pressure and temperature arebeing monitored. Even apparatuses that cannot directly monitor imagequality, such as the foreign matter inspection apparatus, can performinspection with the signal intensity always kept at the maximum level.

According to this embodiment, the complicated focus adjustment task thatwould otherwise need to be performed about once per hour in three toeight minutes is eliminated, improving the availability of theapparatus.

This embodiment relates to focus adjustment in a foreign matterinspection apparatus that has the features described above and inspectsforeign matter on a wafer.

FIG. 1 is a drawing to show the schematic structure of the foreignmatter inspection apparatus of this embodiment.

FIG. 10 is a drawing to show the schematic structure of the foreignmatter detection optical system and the structure of the focus detectionoptical system of the foreign matter inspection apparatus.

FIG. 11 is a block diagram of an embodiment for compensating for anatmospheric pressure and temperature.

The embodiment of the foreign matter inspection apparatus comprises astage unit 300 having an X stage 301, Y stage 302, Z stage 303, and θstage 304 on which a wafer 1 to be inspected is mounted as well as astage controller 305, a illumination optical system 100 having a laserlight source 101 etc., illumination beam spot imaging units 110, 120,and 130, an foreign matter inspection optical system 200 having aobjective lens 201, spatial filter 202, imaging lens 203, varifocal lensgroup 204, and a one-dimensional detector (image sensor) 205 such as aTDI sensor, and a control system 400 having a signal processing system402, an output unit for storing defect detection results such as forforeign matter and delivering the defect detection results, acalculation processing system 401 for controlling the driving of a motoretc., coordinates, and sensors, a display system 403, and an inputsystem 404.

Other reference numerals are indicating as followings. 1500: focusdetection optical system, 1501: focus detection light source, 1502:focus detection phototransmitting optical system, 1503: photorecevingoptical system, 1504: focus detection sensor, 1505: focus signalprocessing unit, 1600: atmospheric pressure and temperature sensorsystem, 1601: atmospheric pressure sensor, 1602: atmospheric pressuredata logger, 1603: temperature sensor, 1604: temperature data logger.

The three illumination beam spot imaging units 110, 120, and 130 arestructured so that lights emitted from the laser light source 101illuminate the wafer 1 to be inspected from three directions.

The inspection optical system 200 is structured so that light producedfrom the wafer 1 is detected by a detection lens (objective lens) 201,the spatial filter 202 that shields a Fourier transformed image due toreflected and diffracted light from a repetition pattern, the imaginglens 203, and the one-dimensional detector 205 such as a TDI sensor.

For a stage operation during inspection, the X stage 301 and Y stage 302are driven to perform illumination scanning on illumination beam spotsover the entire surface of the wafer 1 under inspection.

For focus control during inspection, the focus detection optical system1500 detects a position on the surface of the wafer 1 that is undergoingillumination scanning, and transfers a detected position signal to thefocus signal processing unit 1505. The focus signal processing unit 1505converts the position signal to the amount of movement of the Z drivingapparatus 303 a and transfers the converted signal to the Z stagecontrol unit 305 a.

The Z stage control unit 305 a then drives the Z driving apparatus 303a, and the Z stage 303 moves up and down so that a fixed distance ismaintained between the objective lens 201 and the surface of the wafer1.

The distance between the objective lens 201 and the surface of the wafer1 can be arbitrarily controlled by setting an offset in the Z stagecontrol unit 305 a.

In this embodiment, focus variations caused by changes in atmosphericpressure and temperature are controlled as offsets given to the Z stagecontrol unit 305 a.

Next, a procedure for compensating for focus variations in thisembodiment will be explained.

At first, an example of temperature compensation will be used to explaina flow of compensation.

FIG. 12 is a graph to indicate temperature variations and changes in thefocus Z coordinate when temperature is not compensated.

The focus Z coordinate is the Z coordinate at which the signal intensityis maximized, which is obtained by the focus adjustment task.

The temperature was changed step by step by a temperature controlledbath. The atmospheric pressure is constant.

Accordingly, FIG. 12 was obtained by performing the focus adjustmenttask repeatedly at different temperatures.

FIG. 13 a graph to indicate the relation between the temperature and thefocus Z coordinate.

The temperature and focus Z coordinate can be represented as a linearfunction. It can be seen that the focus Z coordinate changes by −1.80 μmeach time the temperature changes by 1° C. This value is saved as atemperature coefficient.

The temperature coefficient takes various values for different opticalsystem structures.

FIG. 14 is a graph to indicate temperature variations and Z compensatedvalues for temperatures.

A Z compensated value for a temperature is obtained from the equationbelow.Z compensated value for temperature=Z reference value+(temperaturecoefficient×(temperature reference value−temperature at arbitrary pointof time))

That is, in the characteristics in FIG. 12, the Z reference value andtemperature reference value were obtained at time T1; values after T1were calculated as Z compensated values. That is, the focus Z coordinatevalue is obtained by calculation without having to performing thecomplicated focus adjustment task.

FIG. 15 a graph obtained by subtracting the characteristics in FIG. 12from the characteristics in FIG. 14. That is, FIG. 15 indicates focuserror in Z compensation for temperatures.

Remaining compensation error is caused due to deviation from the linearfunction between the temperature and the focus Z coordinate.

Focus error due to the Z compensation for temperatures is 0.1 μm orless, which is sufficiently small and is not problematic in practicaluse.

Next, an example of atmospheric pressure compensation will be used toexplain a flow of compensation. A procedure for this compensation is thesame as the procedure for temperature compensation.

FIG. 16 a graph to indicate atmospheric pressure variations and changesin the focus Z coordinate when atmospheric pressure is not compensated.

Changes in atmospheric pressure were obtained as changes in weather.Temperature was kept constant in a temperature controlled bath.

FIG. 17 is a graph to indicate the relation between the atmosphericpressure and the focus Z coordinate.

The atmospheric pressure and focus Z coordinate can be represented as alinear function. It can be seen that the focus Z coordinate changes by+0.12 μm each time the atmospheric pressure changes by 1 hPa. This valueis saved as an atmospheric pressure coefficient.

The atmospheric pressure coefficient also takes various values fordifferent optical system structures.

FIG. 18 is a graph to indicate atmospheric pressure variations and Zcompensated values for atmospheric pressures.

A Z compensated value for an atmospheric pressure is obtained from theequation below.Z compensated value for atmospheric pressure=Z referencevalue+(atmospheric pressure coefficient×(atmospheric pressure referencevalue−atmospheric pressure at arbitrary point of time))

That is, in the characteristics in FIG. 16, the Z reference value andatmospheric pressure reference values were obtained at time T2; valuesafter T2 were calculated as Z compensated values.

FIG. 19 is a graph obtained by subtracting the characteristics in FIG.16 from the characteristics in FIG. 18. That is, FIG. 19 indicates focuserror in Z compensation for atmospheric pressures.

Remaining compensation error is caused due to deviation from the linearfunction between the atmospheric pressure and the focus Z coordinate.

Focus error due to the Z compensation for atmospheric pressures is 0.1μm or less, which is sufficiently small.

Next, an arrangement for compensation will be explained.

FIG. 11 is a block diagram of an embodiment for compensating for anatmospheric pressure and temperature.

An atmospheric pressure measured by the atmospheric pressure sensor 1601at an arbitrary point of time is stored in the atmospheric pressure datalogger 1602.

A temperature measured by the temperature sensor 1603 at an arbitrarypoint of time is stored in the temperature data logger 1604.

Stored in the control CPU 401 are a Z coordinate (Z reference value) atwhich a maximum sensitivity is obtained, an atmospheric pressure(atmospheric pressure reference value) at that point of time, atemperature (temperature reference value) at that point of time, thecoefficient (atmospheric pressure coefficient), which is obtained inadvance so as to convert atmospheric pressures to Z coordinates, and thecoefficient (temperature coefficient), which is also obtained in advanceso as to convert temperatures to Z coordinates.

In compensation for atmospheric pressure variations, a differencebetween an atmospheric pressure measured at an arbitrary point of timeand the atmospheric pressure reference value is taken, the difference ismultiplied by the atmospheric pressure coefficient to obtain a Zconverted value for the difference, and the Z converted value for theatmospheric pressure is added to the Z reference value, yielding a Zcompensated value.

In compensation for temperature variations, a difference between atemperature measured at an arbitrary point of time and the temperaturereference value is taken, the difference is multiplied by thetemperature coefficient to obtain a Z converted value for thedifference, and the Z converted value for the temperature is added tothe Z reference value, yielding a Z compensated value.

Compensation for atmospheric pressure variations and compensation fortemperature variations are performed separately.

Accordingly, when a Z compensated value for an atmospheric pressure andanother Z compensated value for a temperature are added to the Zreference value to obtain a Z compensated value, the atmosphericpressure and temperature can be compensated for at the same time.

The obtained Z compensated value is sent to the Z stage control unit 305a, and an offset is given to the focus following operation performed bythe Z stage 303.

The offset given to the focus following operation provides the effectthat variations in focus caused by changes in atmospheric pressure andtemperature are corrected.

As described above, when control is performed, variations in focuscaused by changes in atmospheric pressure and temperature are corrected.

1. An inspection apparatus comprising: an irradiating unit whichirradiates an object with light; a detection unit which detects lightfrom the object, the detection unit including a heat radiating unit toaccommodate a sensor therein for detecting the light from the object andpromote heat loss of the sensor; and a temperature-controlled partaccommodating section which accommodates at least one of an objectivelens and an auto focus unit therein and controls a temperature of atleast one of the objective lens and auto focus unit at a predeterminedtemperature.
 2. The inspection apparatus according to claim 1, whereinthe temperature-controlled part accommodating section comprises: atemperature controlling unit which controls the temperature of at leastone of the objective lens and the auto focus unit accommodated in thetemperature-controlled part accommodating section.
 3. The inspectionapparatus according to claim 2, wherein the temperature controlling unitcontrols the temperature of a medium which is supplied to thetemperature-controlled part accommodating section.
 4. The inspectionapparatus according to claim 3, wherein the medium is air, pure water,fluorine-based inert liquid, hydro fluoro ether (HFE), or ethyleneglycol.
 5. The inspection apparatus according to claim 3, wherein: thetemperature controlling unit is connected to the heat radiating unit viaa pipe and a heat insulating valve which is provided on the pipe, andthe temperature controlling unit operates the heat insulating valve touse heat from the heat radiating unit so as to control temperature ofthe medium.